Marked enhancement of Néel temperature in strained YMnO₃ thin films probed by femtosecond spectroscopy

In this paper, the (001)-oriented hexagonal YMnO₃ (h-YMO) thin films with various nominal strain states were deposited on MgO(100), MgO(111) and YSZ(111) substrates by pulsed laser deposition. The ultrafast dynamics probed by wavelength-tunable femtosecond pump-probe spectroscopy was performed to disclose the effects of the epitaxial strain on the electronic structure and associated magnetism. Analyses based on the measured transient-reflectivity- change (ΔR/R) curves revealed that while the magnitude of the on-site Mn d-d transition energy E_dd(T) changes only slightly with the variation of the lattice constant ratio c/a, a marked shift in the antiferromagnetic (AFM) Néel temperature T_N was observed and the direction of shift was dependent on the type of strain. The possible mechanism for the observed strain effect on the AFM ordering is discussed.